Electronic power supplies are known in the art. There are occasions where it is necessary to adjust some of the working parameters of the power supply such as the output voltage, the supplied current and so on. This is commonly done by applying an analog input signal to the analog input of an adjustable power supply module. For example, an adjustable power supply module capable of supplying voltage up to 100 V will produce its maximum voltage when applying 10 Volts to its analog control input while application of 5 volts to the analog control input will cause the power supply module to produce only 50 Volts. Adjustable power supply module is disclosed in a patent application filed by the inventors of the present invention.
It is sometimes advantageous to electronically isolate the controlling analog input signals from the power supply and load. This is done to protect the low voltage controlling circuits against fluctuations in the common potential used for the load and power supply circuits, fluctuations that may be caused by large ground loop currents or large current or voltage variations that may exist in the load and power supply circuits.
The isolation problem becomes more acute when the controlling system is remote or must control several power supplies. In these systems, it is important to prevent collapse of the controlling system due to a failure of one power supply unit, a failure that might cause the load circuit to transmit voltages or current high enough to damage the controlling system. Isolation requirements of few hundreds to few thousands volts are often requested.
Analog isolators are frequently used for the abovementioned purposes; however, these analog isolators are highly expensive.
Several standards are used to form the relation between the control input signals and the power supply operation, for example: the analog control signal may be applied in the form of current instead of voltage or the analog input signal may be the application of specific resistance between input terminals of the power supply module.
In addition, some power supply modules are equipped with an analog monitoring output for monitoring their operation. For example, it may be useful to monitor the current drawn by the load. A monitoring analog output producing an analog output signal of a voltage proportional to the current drawn by the load may be connected to a display unit for displaying and monitoring the supplied current. For proper isolation, all analog inputs and analog monitoring outputs have to be isolated.
In order to properly adjust and correctly monitor the operation of an adjustable power supply unit, it is necessary to provide the power supply unit with the correct analog control input signals and to be able to translate the analog monitoring output signal for meaningful interpretation of the power supply working parameters. Since several standards and proprietary translation methods are used in the industry, hardware alterations are needed to set up a power supply module for its specific use. Setting up may be done at manufacturing by soldering components (usually resistors) of specific values, or in the field by configuring the system using switches and jumpers to select the desired value among several preinstalled components. These methods limit the flexibly of the system, are time consuming and necessitate manual handling of the system which may be hazardous when done by untrained user.
For example; Xantrex Technology manufactures the XPR series of analog-controlled power supplies for applications including burn-in, electroplating, battery charging, and steering magnets.
Analog control comes standard with the XPR Series as resistive or voltage programming of the supply output voltage and current limits.
Several models are available with voltage ranges of 0–3 up to 0–30 KV and maximum current of 1 A up to 60 KA.
Standards used for analog inputs are set at the factory and selected among: Voltage input of 0–5 V or 0–10 V for full range of the supply output, resistance input of 0–5 k or 0–10 k for full range of the supply output.
Analog monitoring signal proportional to the actual output voltage and current of the power supply is provided using one of two factory-defined standard of 0–5 V or 0–10 V for full range.
It is clear to see that a user analog input signal may produce undesirable supply output if the wrong signaling standard is used.
The series has a straightforward front panel, featuring a seven segment LED display with several status and alarm indicators, and 10-turn knobs for voltage and current control. The front panel buttons allow users to conveniently set and view the over voltage protection set points, view the output voltage and current limits, enable output shutdown, and offer the flexibility of toggling control of the power supply between the front panel and remote analog control.
Lambda EMI, Inc. includes isolation option as add-on card to some of its power supplies, for example the Genesys series. IS510 is a voltage mode isolator with factory pre-selected range 0–5 or 0–10 V for both input and monitoring channel. IS4200 is a current mode isolator with a range of 4–20 mA for both input and monitoring channel. Both models offer accuracy of +/−1% for the input signals and +/−1.5% accuracy for the monitoring signals.